What is the
I want to
realistic.
Pat,
Atlas-O specifies their 3-rail curve sizes the same way 2-railers do, center-rail to center-rail. This is different than most tin-plate track where the diameter is specified from outside tie edge to opposite outside tie edge.
A quick rule-of-thumb is add 1-1/4" to the Atlas-O size to get the "tinplate" measurement. So Atlas-O O27 curves would actually be O28-1/4 using the tinplace specification method.
-- Len Head Rust Scraper KL&B Eastern Lines RR Museum